Hi all, My first post and I have been reading this forum and website all yesterday and most of the night. Exhausted today and still feel totally out of my depth.
Is there anybody that would be interested in providing me a design service please.
I have an off grid system. 12.5KW. 2 x SMA grid tie inverters (SunnyBoy) and 2 Sunny Island 5048 plus a huge battery bank.
This is my understanding:
At present when the the sunny boy is producing more energy than is being consumed the sunny island will increase the the frequency of the grid. This tells the Sunny boy to derate. (waste energy). I would like this energy to be used to heat water.
This is most likely to happen when the batteries are nearing fully charged and the charging side reduces the required power.
However, it can also happen when the batteries are much lower if the energy being produced is higher the maximum permissible charging current.
Is there a way to monitor the current going to the batteries (on both Sunny Islands), the power being consumed by the house and compare that with the power being generated by the sunnyboys. Then if there is excess energy available divert power to a load. in my case the immersion heater.
I am pretty good with electrics and electronics so am fine with soldering circuit boards etc. At least I thought I was until reading the complicated stuff going on in the designs on here! Although if anybody would like to provide the full design and build service I would be delighted.
I have looked at all the commercial solutions and none of them are suitable. They all seem to only work on systems connected to the national grid. They do not take into account the fact that excess energy depends on the usage in my home AND the battery charging combined. Many are also not intelligent and are based only on a fixed threshold and simply switch on/off when that that threshold is crossed.
Many thanks, James
Re: Wanted: person to build a solution for me. Off grid power diversion solution.
Hi James,
Welcome.
I have a similar sort of setup, but using Sunny backups, but I'm grid connected. I'm still setting up my system but I am thinking of measuring the frequency and using that for switching the loads when I am disconnected from the grid eg power cut.
I'm not sure on the response times within the SMA hardware to changes but I could imagine they are pretty quick!
Re: Wanted: person to build a solution for me. Off grid power diversion solution.
Thanks fior your reply.
Yes I wondered about doing that too I but couldnot find a frequency reactive relay.
Will any of the openenergymonitor devices perform this task?
The other complication with my system is that the frequency also changes when the generator runs. And it is made worse as the faster the geni runs the higher the frequency. So the SMA devices think they should derate, so the geni works harder, so the frequnecy increases......, and so on until the geni is doing all of the work. That's a failing in the SMA design I think but their stance is that the generator should be fixed at 50hz even though no generators seem to be capable of achieving this under varying loads. Very frustrating. It even causes the clock on our oven to speed up and slow down!
Re: Wanted: person to build a solution for me. Off grid power diversion solution.
Martin\r's PLL controller is capable of measuring frequency. Frequency is not an input into the control algorithm, though if you can come up with an algorithm, I don't see why it should not be an input.
Re: Wanted: person to build a solution for me. Off grid power diversion solution.
I bought a relay on ebay but the only thing with just using that is that as soon as the relay turns the load on the frequency will drop to bringing the sunny boys back up to power and then the relay will drop out again. You could put a delay timer in.
I'm sure using an Arduino solution will be much better, but my programing skills are not up to it yet!!
I have an exmilitary generator and the control system on that is absolutely spot on but very very complicated with reverse power detection and paralleling etc. You really need electronic speed control rather than mechanical and an adequately or oversized generator for your loads so it doesn't struggle.
Re: Wanted: person to build a solution for me. Off grid power diversion solution.
I think what you're saying is it is much better to regulate the engine speed directly by governing the fuel input, rather than by loading it via the generator, and I entirely agree. That's not to say it would be impossible to use the emonTx/Arduino to do both, but the two functions - generator speed control and energy diversion - are quite separate and should really remain so.
You will need proportional control. A relay is bound to hunt and lead to instability.
Re: Wanted: person to build a solution for me. Off grid power diversion solution.
Yes, on mine the electronic speed control is done on the injector pump and the speed is sensed with an inductive pickup on the flywheel. In the photo attached you can see the link rod from the actuator to the injector pump. For those wondering the starter motor in the photo is a hydraulic backup one for if the batteries are flat, typical military. Excellent for fitness training!!
Re: Wanted: person to build a solution for me. Off grid power diversion solution.
I'm in the solar trade. Been working designing and building solar energy systems for 4 years now. We have done many systems just like the one you have. There are some settings that need to be correctly set. Bust out your SI manual and lets work this out. First off your Max Sell from the SI's are 5000 W. Here is a link to the install manual if you need. http://www.sma-america.com/en_US/products/off-grid-inverters/sunny-island-4548-us-6048-us.html
First off to clarify, I do NOT know your locality and you should know the limits of your electrical code to keep you safe and linesmen safe. I live in Virginia, US, so i'll be referring to what I know.
The SMA support line is awesome and will help you set this up also. Without knowing exactly how you wired the thing i am going to assume somethings. First you have grid connected to the SI's so than you "could" charge using grid power and second you have a automatic transfer switch for your Generator. And you use the Relay's built into the SI's to control the Gen.
Some basic settings need to be changed--- setting 231 #05 set to GenGrid ---- 232 #08 Gridfeed--- 232 #GrRvPwr 5000 "default is 100"
start looking into the SI's settings because it is Completely capable of selling\passing all the excess PV power to the Loads of the house.
PS. there is anouther way that has workedfor us. We do this when we use only 1 SI. You can place a contactor that switches between grid and offgrid. Some things may need to be changed in the SB though. basically when you have grid power the SI's are charged using grid power and the SB are also Grid tied. so indirectly the SB's and charging the battery bank.
Hope this helps
Shine on,
bernie
Re: Wanted: person to build a solution for me. Off grid power diversion solution.
It may be worth having a look at;
http://ambercontrol.com/index.php/amber-switch
Its not cheap but could give you some ideas.